Proposed solutions for 2021 day 23

2021/puzzle-23-01.cc

@@ -0,0 +1,199 @@
+#include <array>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <set>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+
+// Map:
+// #############
+// #ab.c.d.e.fg#
+// ###h#i#j#k###
+//   #l#m#n#o#
+//   #########
+//
+//  a -1- b -2- c -2- d -2- e -2- f -1- g
+//         \   / \   / \   / \   /
+//          2 2   2 2   2 2   2 2
+//           +     +     +     +
+//           h     i     j     k
+//           |     |     |     |
+//           1     1     1     1
+//           |     |     |     |
+//           l     m     n     o
+
+using Position = char;
+using UInt = int;
+using Type = char;
+
+std::multimap<Position, std::pair<Position, UInt>> costs{
+  {'a', {'b', 1}}, {'b', {'a', 1}}, {'b', {'c', 2}}, {'b', {'h', 2}}, {'c', {'b', 2}},
+  {'c', {'d', 2}}, {'c', {'h', 2}}, {'c', {'i', 2}}, {'d', {'c', 2}}, {'d', {'e', 2}},
+  {'d', {'i', 2}}, {'d', {'j', 2}}, {'e', {'d', 2}}, {'e', {'f', 2}}, {'e', {'j', 2}},
+  {'e', {'k', 2}}, {'f', {'e', 2}}, {'f', {'g', 1}}, {'f', {'k', 2}}, {'g', {'f', 1}},
+  {'h', {'b', 2}}, {'h', {'c', 2}}, {'h', {'l', 1}}, {'i', {'c', 2}}, {'i', {'d', 2}},
+  {'i', {'m', 1}}, {'j', {'d', 2}}, {'j', {'e', 2}}, {'j', {'n', 1}}, {'k', {'e', 2}},
+  {'k', {'f', 2}}, {'k', {'o', 1}}, {'l', {'h', 1}}, {'m', {'i', 1}}, {'n', {'j', 1}},
+  {'o', {'k', 1}}};
+
+std::map<Type, UInt> multipliers{{'A', 1}, {'B', 10}, {'C', 100}, {'D', 1000}};
+
+struct State
+{
+  auto finished() const noexcept -> bool { return nodes_ == finished_; }
+  auto size() const noexcept -> UInt { return 15; }
+  auto node(unsigned idx) noexcept -> Type& { return nodes_[idx]; }
+  auto node(unsigned idx) const noexcept -> Type const& { return nodes_[idx]; }
+
+  bool check_move(unsigned from, unsigned to)
+  {
+    if (nodes_[from] == '.' || nodes_[to] != '.') {
+      return false;
+    }
+    if (from > 10) {
+      // Only move out of the bottom row if we're not meant to be here.
+      return nodes_[from] != finished_[from];
+    }
+    if (from > 6 && from < 11) {
+      if (to > 10) {
+        // Only move into bottom position if we're moving the correct piece.
+        return nodes_[from] == finished_[to];
+      }
+      // Moving to top row - anything allowed.
+      return true;
+    }
+    if (from < 7) {
+      if (to < 7) {
+        return true;
+      }
+      // Can only move down if we're the right type.
+      return nodes_[from] == finished_[to];
+    }
+    abort();
+  }
+
+  bool move(unsigned from, unsigned to)
+  {
+    if (!check_move(from, to)) {
+      return false;
+    }
+    std::swap(nodes_[from], nodes_[to]);
+    return true;
+  }
+
+  constexpr bool operator<(State const& rhs) const noexcept { return nodes_ < rhs.nodes_; }
+  constexpr bool operator==(State const& rhs) const noexcept { return nodes_ < rhs.nodes_; }
+
+private:
+  std::array<Type, 15> nodes_{'.'};
+  static std::array<Type, 15> finished_;
+};
+
+template<>
+struct std::hash<State>
+{
+  auto operator()(State const& key) const -> std::size_t
+  {
+    std::size_t result{0};
+    for (auto i{0}; i < 15; ++i) {
+      result <<= 3;
+      if (key.node(i) != '.') {
+        result |= key.node(i) - 'A' + 1;
+      }
+    }
+    return result;
+  }
+};
+
+std::array<Type, 15> State::finished_ = {'.', '.', '.', '.', '.', '.', '.', 'A',
+                                         'B', 'C', 'D', 'A', 'B', 'C', 'D'};
+
+auto main() -> int
+{
+  std::regex line2_re{R"(#(.)(.)\.(.)\.(.)\.(.)\.(.)(.)#)"};
+  std::regex line3_re{"###(.)#(.)#(.)#(.)###"};
+  std::regex line4_re{"#(.)#(.)#(.)#(.)#"};
+
+  std::string line;
+  std::smatch m;
+  std::getline(std::cin, line);
+  if (line != "#############") {
+    std::cerr << "Incorrect first line.\n";
+    return 1;
+  }
+  State initial_state;
+
+  std::getline(std::cin, line);
+  if (!std::regex_search(line, m, line2_re)) {
+    std::cerr << "Unable to match line 2 " << line << '\n';
+    return 1;
+  }
+  for (unsigned i = 0; i < 7; ++i) {
+    initial_state.node(i) = m.str(i + 1)[0];
+  }
+
+  std::getline(std::cin, line);
+  if (!std::regex_search(line, m, line3_re)) {
+    std::cerr << "Unable to match line 3 " << line << '\n';
+    return 1;
+  }
+  for (unsigned i = 0; i < 4; ++i) {
+    initial_state.node(7 + i) = m.str(i + 1)[0];
+  }
+
+  std::getline(std::cin, line);
+  if (!std::regex_search(line, m, line4_re)) {
+    std::cerr << "Unable to match line 4 " << line << '\n';
+    return 1;
+  }
+  for (unsigned i = 0; i < 4; ++i) {
+    initial_state.node(11 + i) = m.str(i + 1)[0];
+  }
+
+  std::map<State, UInt> states;
+  states.insert({initial_state, 0});
+  std::set<State> visited;
+
+  while (!states.empty()) {
+    auto it{std::min_element(states.begin(), states.end(), [](auto const& lhs, auto const& rhs) {
+      return lhs.second < rhs.second;
+    })};
+    if (visited.size() % 10'000 == 0) {
+      std::cout << "Visited: " << visited.size() << " number of states: " << states.size()
+                << " Min energy: " << it->second << '\n';
+    }
+
+    State state{it->first};
+    UInt cost{it->second};
+    visited.insert(state);
+    states.erase(state);
+
+    if (state.finished()) {
+      std::cout << "Done with cost " << cost << '\n';
+      return 0;
+    }
+
+    for (unsigned i = 0; i < state.size(); ++i) {
+      if (state.node(i) == '.') {
+        continue;
+      }
+      auto [it_begin, it_end] = costs.equal_range(i + 'a');
+      for (auto cost_it{it_begin}; cost_it != it_end; ++cost_it) {
+        State next_state{state};
+        if (next_state.move(i, cost_it->second.first - 'a') && !visited.contains(next_state)) {
+          UInt next_cost = cost + cost_it->second.second * multipliers[state.node(i)];
+          auto [insert_it, success] = states.insert({next_state, next_cost});
+          if (!success) {
+            insert_it->second = std::min(insert_it->second, next_cost);
+          }
+        }
+      }
+    }
+  }
+
+  std::cerr << "FAILED\n";
+  return 1;
+}